As is known in the art, printed circuit boards generally include conductive outer layers. Such outer layers are typically provided using a subtractive etching process. That is, the processing of the printed circuit board is begun with a full sheet of copper and selective portions of the copper are removed using a subtractive etching process. Any desired holes are then drilled on the printed circuit board. Electroless and electrolytic plating techniques may then be used to metalize the holes. In a subtractive etching process, it is relatively difficult to maintain the relatively small tolerances (i.e line width, etc. . . . ) required to manufacture printed circuit boards.
As is also known in the art, there has been a trend to reduce the size of electronic components and provide printed circuit boards having multi-chip modules etc. . . . This results in a need to increase the number of components such as surface mount components provided on a printed circuit board. This results in a so-called "densely populated" or simply "dense" printed circuit board. One problem with making such dense printed circuit boards is that the yield from the manufacture of such boards is relatively low. This low yield is due, in part, to the fact that such printed circuit boards are manufactured using a subtractive etching process in which it is relatively difficult to maintain predetermined tolerance ranges.
As is also known, in the conventional subtractive etching approach half-ounce copper is often disposed on the raw substrate and after lamination and subsequent drilling processes are performed, the substrate is then plated using one ounce of conductive plating. In those applications which require plated through holes, the plating is added and the metalized holes are provided having one ounce of copper therein while the plated surface of the substrate, is provided having one and one-half ounces of copper. This makes it more difficult to provide a solder connection in the plated through hole because the additional copper on the surface of the plated-through hole reduces the capillary action of the post soldering process.
Thus using the conventional approach, printed circuit boards have been manufactured using a drill and plate up technique. Such through-hole metalization techniques have become standard within the industry. One problem with such techniques, however, is that subtractive process must be performed on the external layer to provide external layer conductor definition.